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<br />SLOPE STABILITY REPORT <br />DELTA SAND AND GRAVEL <br />PIT #1 AMENDMENT <br />by: Greg Lewicki, P.E. <br />July 27, 2002 <br />1 INTRODUCTION <br />This slope stability analysis is for the final configuration of the slopes in the amendment <br />area. The post-mining use of the area is a lake for water-skiing althoagh all areas will be <br />seeded and mulched using a dryland mix. Slope stability is important since there will be <br />some residential buildings within a relatively short distance of the north property line in the <br />amendment area. I, Greg Lewicki, am a registered P.E: in the State of Colorado with over <br />25 years experience in all forms of embankment design, backfill slope stability and <br />reclamation. <br />2. PLAN OF OPERATIONS AND DETERMINATION OF FINAL SLOPE SAFETY <br />FACTOR <br />Currently, most of the overburden from the azea to be mined has been excavated and <br />stockpiled to form a perimeter berm around the outside edge of the lake azea. See enclosed <br />cross-section sketch. The plan is to mine the gravel to a depth of approximately 22-27' deep <br />from the surface, leaving a steep grade of 1/2H:1V. Since the natural water level is <br />expected to be 18' from the pit floor once pumping is stopped, the majority of the reclaimed <br />slope will be under water. For reclamation, the upper part of the slope will be cut with a <br />dozer to a 3H1V slope and used to backfill the lower part of the slope to 3H:1V. This <br />material will be compacted with the dozer to the extent that this material can be compacted. <br />The gravel material has Less than 5% fines (-200 mesh) therefore, this material gets its <br />strength from internal angle of friction, not cohesion. Most of the material is somewhat <br />rounded or slightly angular. <br />Under the Unified Classification, this material would be classified as GP, or poorly graded <br />clean gravels or gravel/sand mixture, with an approximate internal angle of friction of 37 <br />degrees. For materials with no cohesion, the slope safety factor is the internal angle of <br />friction divided by the slope angle in degrees. For this case, a 3H:1V slope is 18.3 degrees, <br />therefore, the slope SF = 37/18.4 = 2.0. This safety factor is more than adequate to prevent <br />lope failure. <br />The overburden from the berms will be placed on the final 3H:1V slope for reclamation. <br />